The Senate voted 60 to 37 to approve $2 billion in additional funding Thursday, ending a weeklong scramble to keep the popular auto rebate initiative from running out of money. That could subsidize the purchase of half a million vehicles and provide a further boost to the sagging auto industry.

Heavy demand is already leading to scattered shortages of some hot-selling vehicles, such as the Toyota Prius, Ford Focus and Dodge Caliber. Chrysler Group and General Motors Co., which shut down many of their factories for several weeks this summer to save money and reduce inventories, have been particularly affected.

"Business had slowed so much that a lot of dealers had reduced their inventories because it was expensive to hold on to," said Jerry Key, general manager at Capistrano Ford. "But now that we've had this surge in business, there's going to be holes in the inventory."